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From: Nick Bostrom <bostrom.domain.name.hidden>

Date: Tue, 20 Apr 1999 21:10:24 +0000

*> Date: Sat, 17 Apr 1999 17:03:16 -0400
*

Jacques M Mallah wrote:

*> Suppose he'd have kids if on a certain measurement he
*

*> saw spin up.
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*> If you draw many spins from a sample and they are found to be 50%
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*> up and 50% down, you can be reasonably sure that the quantum probability
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*> p to measure up is about 50%.
*

Yes, you are right that on the MWI, if Adam thinks there is a

substantial probability that the q.m. chance of a deer appearing is

substantial, then you wouldn't get the shift that the paper refers

to. And as you say, Adam could obtain evidence for the hypothesis

that the q.m chance is substantial from observing his situation. Of

course, this presupposes that we have managed to make sense of the

MWI so that it gives probabilities in agreement with q.m. even when

combined with the self-sampling assumption. This is not trivial. If

q.m. says that outcome A has probability 2/3 and ¬A has probability

1/3, then there would have to be twice as many Adams observing A as

¬A. Moreover, the total number of Adams at any time should be roughly

constant (modulo such events as Adam dying). It wouldn't do, for

example, to just think of Adam as splitting everytime a measurement

is made, for then almost all Adams would live very near the

temporal end of the universe (if there is one). So it seems we would

have to postulate an infinite (and uncountable) number of worlds. But

then it is not easy to see how the SSA applies -- there would always

be an infinite number of worlds where Adam is observing A and an

equally large infinite number of worlds where he is observing ¬A.

Nick Bostrom

http://www.hedweb.com/nickb n.bostrom.domain.name.hidden

Department of Philosophy, Logic and Scientific Method

London School of Economics

Received on Tue Apr 20 1999 - 13:12:28 PDT

Date: Tue, 20 Apr 1999 21:10:24 +0000

Jacques M Mallah wrote:

Yes, you are right that on the MWI, if Adam thinks there is a

substantial probability that the q.m. chance of a deer appearing is

substantial, then you wouldn't get the shift that the paper refers

to. And as you say, Adam could obtain evidence for the hypothesis

that the q.m chance is substantial from observing his situation. Of

course, this presupposes that we have managed to make sense of the

MWI so that it gives probabilities in agreement with q.m. even when

combined with the self-sampling assumption. This is not trivial. If

q.m. says that outcome A has probability 2/3 and ¬A has probability

1/3, then there would have to be twice as many Adams observing A as

¬A. Moreover, the total number of Adams at any time should be roughly

constant (modulo such events as Adam dying). It wouldn't do, for

example, to just think of Adam as splitting everytime a measurement

is made, for then almost all Adams would live very near the

temporal end of the universe (if there is one). So it seems we would

have to postulate an infinite (and uncountable) number of worlds. But

then it is not easy to see how the SSA applies -- there would always

be an infinite number of worlds where Adam is observing A and an

equally large infinite number of worlds where he is observing ¬A.

Nick Bostrom

http://www.hedweb.com/nickb n.bostrom.domain.name.hidden

Department of Philosophy, Logic and Scientific Method

London School of Economics

Received on Tue Apr 20 1999 - 13:12:28 PDT

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